1. Field of the Invention
The present invention relates generally to communication over Ethernet-Class network and, more specifically to encoding methods for robust communication over noisy communications media.
2. Background
The vision of the networked home has driven many a business plan, but product offerings to date have been too limited in capability or in market potential to achieve the dream. Home networking is different than networking in the workplace. The applications are different, the traffic patterns are different, and the media available to carry the data are different. Certainly home networking users will want to transfer files between their computers and share peripherals such as printers. They will want gateways to broadband access so they can share their Internet connection between multiple devices. Users will also want other services, such as voice-over-IP (VoIP), streaming media for entertainment, and support for multi-player networked games.
While some newer houses are wired with cables suitable for Ethernet, most are not. This limits the choices for home network physical medium to phone wiring, wireless, and power line, each presenting a mixed bag of attributes.
There has been a proliferation of wireless networking and related components in recent years. However, wireless communication suffers from blind spots in certain areas of the home requiring equipment that is expensive and sophisticated, and maybe some technical acumen not available to the average homeowner.
Telephone line networking is also taking hold. However, many households lack phone jacks at convenient locations to achieve the foreseeable benefits of home networking. For instance, some older houses may only have one phone jack located in the kitchen for use in the kitchen and other living areas (e.g. living room, family room, etc). Thus, it may be inconvenient or messy to provide network connections to remote devices. Power plugs, on the other hand, are located virtually in every room in the home. And some homes have multiple power outlets located in every corner of every room. However, the power line appears to be the most difficult medium of these three for communication, but it does have two appealing attributes. First, as with phone lines, no RF conversion hardware is needed and, thus, the cost can be low compared to wireless solutions. But more importantly, power outlets are almost everywhere someone might want to use a networked device at home.
The power line medium is a harsh environment for communication. For instance, the channel between any two outlets in a home has the transfer function of an extremely complicated transmission line network with many stubs having terminating loads of various impedance. Such a network has an amplitude and phase response that varies widely with frequency. At some frequencies the transmitted signal may arrive at the receiver with relatively little loss, while at other frequencies it may be driven below the noise floor. Worse, the transfer function can change with time. This might happen because the homeowner has plugged a new device into the power line, or if some of the devices plugged into the network have time-varying impedance. As a result, the transfer function of the channel between outlet pairs may vary over a wide range. In some cases, a broad swath of bandwidth may be suitable for high quality transmission, while in other cases the channel may have a limited capacity to carry data.
Due to these potential frequency variations, efficient use of the power line medium requires an adaptive approach that compensates for the channel transfer function in some way. Fortunately, advances in ASIC density enables the use of sophisticated signal-processing techniques at price points that makes Ethernet-class home networking via power lines a cost-effective reality. Sophisticated ASIC-based signal processing technology makes it possible to keep a lid on the interference and transfer function degradations that compromise the power line transmission medium.
Prior art powerline communication systems include an effective and reliable method of performing adaptation that achieves rates of between 4-21 MHz on typical channels, but which adjusts the bit rate to fight through really harsh channels. In addition to the transfer function problem, and equally significant, interference on the power line must be considered. The most severe interference sources rarely have properties similar to the easily analyzed white Gaussian noise produced by receiver front ends. Instead, the interference can be either impulsive or frequency selective in nature, and sometimes both.
Typical sources of noise are brush motors, fluorescent and halogen lamps, switching power supplies, and dimmer switches. In addition, ingress sources such as amateur band radio transmitters can be significant. The net impact of these different interference sources is that raw received data bits tend to have significant numbers of bit errors, which must somehow be corrected. Prior art powerline technology devices contain a combination of sophisticated forward error correction (FEC), interleaving, error detection, and automatic repeat request (ARQ) capabilities to ensure that the channel appears completely reliable to the network layer protocols.
However, as the size of the home network increases and with bandwidth demands skyrocketing, it is desirable to provide means for robust communication of data in a powerline network environment. Any workable solution for reliable communication on the power line medium must include both a robust physical layer (PHY) and an efficient media access control (MAC) protocol. The MAC protocol controls the sharing of the medium among multiple clients, while the PHY specifies the modulation, coding, and basic packet formats.